1. Field
Embodiments described herein generally relate to methods for fabricating devices on semiconductor substrates. More specifically, embodiments described herein relate to methods of patterning magnetic materials.
2. Description of the Related Art
Microelectronic devices are generally fabricated on a semiconductor substrate as integrated circuits wherein various conductive layers are interconnected to one another to facilitate propagation of electronic signals within the device. An example of such a device is a storage element in magneto-resistive random access memories (MRAM) that facilitate storage of digital information in a form of the direction of magnetization of a magnetic material within the MRAM.
A memory cell in an MRAM device generally is a multi-layered structure comprising a pair of magnetic layers separated by a tunnel layer. More specifically, the MRAM device comprises a free (or top) magnetic layer that may change a direction of magnetization and a bottom magnetic layer that has a fixed direction of magnetization. The magnetic layers are separated by the tunnel layer formed of a non-magnetic dielectric material, such as aluminum oxide (Al2O3), magnesium oxide (MgO), or other similar dielectric materials. The top and bottom magnetic layers may each comprise a plurality of sub-layers of magnetic materials, e.g., permalloy (NiFe), cobalt iron (CoFe), and the like. The top and bottom magnetic layers are also supplied with film electrodes (e.g., comprising tungsten (W), tantalum (Ta), tantalum nitride (TiN), copper (Cu), and the like) to form an electrical connection for the memory cell to the lines of the MRAM.
Fabrication of an MRAM device comprises etch processes in which one or more layers comprising an MRAM film stack are removed, either partially or in total. The MRAM device comprises the layers that are generally formed from materials that may be easily oxidized, sensitive to corrosion or very thin, as well as may leave difficult to remove metal-containing post-etch residues upon the film stack. Such residues may build up along the sides of the film stack. The conductive residues or eroded layers may cause electrical short-circuits within an MRAM device, e.g., between the top and bottom magnetic layers, or may render the MRAM device to operate sub-optimally or not at all.
Various post-etching cleaning methods including wet cleaning processes have been developed for removing conductive residues. During one exemplary wet cleaning process the conductive residues are removed by repeatedly exposing the substrate to cleaning solvents comprising, in various combinations, hydrogen fluoride (HF), ammonium fluoride (NH4F), ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2), and the like. Disadvantages of using the wet cleaning processes to remove residues produced during fabrication of the MRAM devices include an increase reduced productivity of the overall etching process due to the addition of the wet cleaning process, lack of real time end point detection, as well as a need in dedicated processing equipment.
Other post-etching cleaning methods include the use of sulfur based chemistries to sputter away the conductive residues. However, current sulfur based chemistries have been found to adversely affect the tunnel junction layer.
Therefore, there is a need in the art for improved methods for fabricating an MRAM device while reducing the amount of conductive residue produced.